IRBIL, Iraq — The United States sent helicopters into combat against Islamic State targets west of Baghdad on Sunday, the first time low-flying Army aircraft have been committed to fighting in an engagement that the Obama administration officials has promised would not include “boots on the ground.”

The U.S. Central Command, in a statement about U.S. activities against the Islamic State in Iraq and Syria, provided few specifics about the helicopters. They were probably AH-64 Apache attack helicopters, which were deployed to Baghdad International Airport in June to provide protection for U.S. military and diplomatic facilities.

Until Sunday, U.S. airstrikes in Iraq have been limited to fast-moving Air Force and Navy fighter aircraft and drones. But the use of the relatively slow-flying helicopters represents an escalation of American military involvement and is a sign that the security situation in Iraq’s Anbar province is deteriorating. Last week, the Islamic State militants overran numerous Iraqi bases and towns and were becoming a widespread presence in Abu Ghraib, the last major town outside of Baghdad’s western suburbs.

Jeffrey White, a former senior Defense Intelligence Agency analyst who closely follows developments in Iraq, said the use of helicopter gunships by the United States means that U.S. troops effectively are now directly involved in ground battles.

“It’s definitely boots in the air. This is combat, assuming U.S. Army guys were flying the helicopters,” said White, a defense fellow at the Washington Institute for Near East Policy, a center-right policy institute. “Using helicopter gunships in combat operations means those forces are in combat.”

Moreover, the Obama administration’s decision to authorize the use of U.S. helicopter gunships indicates that nearly two months of U.S.-led airstrikes by fixed-wing fighters and bombers have failed to stop the Islamic State from massing ground troops and launching offensive operations, he said.

“It means however we were applying air power previously didn’t work to stop them from putting together offensive actions. One of the hopes was that using air power would impede them from using offensive operations,” White said. “But apparently, they have been successful in doing that despite the airstrikes.”

At the time the Apache squadron was deployed to Iraq, Pentagon officials said the aircraft would be used to protect American military and diplomatic facilities at the airport and the U.S. Embassy in Baghdad.

But the advance by the Islamic State into the Abu Ghraib area just outside the airport complex threatens to put the militants within rocket and artillery range of the facility, which houses hundreds of U.S. military advisers and a joint operations center. Any sustained shelling would likely force the airport to close, posing a hazard not only to American troops working in the joint operations center, but also to plans to evacuate U.S. diplomatic personnel.

Although the administration has repeatedly said that no “ground forces” would be used in the fight against the Islamic State, the use of the AH-64 represents a blurring of that promise.

The helicopters carry two-man crews and, with their missiles and powerful cannons, increase the amount and accuracy of the firepower that the U.S. military can bring to bear against the Islamic State in support of Iraqi ground troops. But because helicopters fly relatively “low and slow,” the Obama administration is taking on greater risk in terms of exposing U.S. forces to casualties, White said.

“The Iraqi air force just lost a brand new Russian helicopter (to Islamic State ground fire). So it’s significantly higher risk for whoever is flying the mission,” White said. “It’s certainly crossing another threshold. The U.S. is conducting strikes that are directly involved in combat.”

In its announcement, Central Command said the U.S. had employed “bomber, fighter and helicopter aircraft” to attack six targets northeast of Fallujah and southeast of Hit, both Islamic State-occupied towns in Anbar. It also said an Islamic State Humvee had been destroyed northeast of Sinjar, in northern Iraq.

In Syria, the Central Command said, U.S. aircraft struck Islamic State positions described as northwest of Mayadin and northwest of Raqqa.